…ield

The Twin struct no longer has an `ip` field (migrated to `relay`/`pk` long
ago), but getTwin/listTwins still did `res.ip = hex2a(res.ip)`. hex2a(undefined)
dereferences `undefined.length`, so every getTwinByID/listTwins call threw
`Cannot read properties of undefined (reading 'length')` on the current runtime.

- Remove the stale `ip` decode from getTwin and listTwins; return the
  metadata-decoded object as-is.
- Harden hex2a to return '' for undefined/null. This is the root of the same
  crash class: hex2a is called on ~16 fields across twin/entity/farms/node/
  tfkvstore, several of which are Option<...> (null) on the current runtime
  (e.g. node serialNumber, publicConfig ipv4/ipv6/gw4/gw6). Null-safe hex2a
  immunizes all of them.
- Add unit tests for hex2a (built-in node:test, no new deps) and wire up the
  `test` script.

Closes #1090

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…uard reads

Live devnet testing (spec 157) surfaced more stale-runtime-assumption bugs in
the read wrappers, beyond the twin `ip` field:

- getEntityIDByName queried `entitiesByNameID` and getEntityIDByPubkey queried
  `entitiesByPubkeyID` — neither exists on the current runtime (renamed to
  `entityIdByName` / `entityIdByAccountID`). Both threw "is not a function".
  These are called by activation-service's createEntity, so createEntity was
  broken against the current runtime. Also normalize not-found to 0 (the new
  storage decodes to null) to preserve the "0 means absent" contract callers rely on.
- getEntity / getNode / getTwin did `res.id` on a null result when the id does
  not exist, throwing "Cannot read properties of null". Guard with `!res` so they
  throw a clean "No such <x>" instead.

All verified live on devnet.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

…g policy name

More stale-structure bugs found while live-verifying getNode/getPricingPolicyById
on devnet (all returned un-decoded hex):

- getNode public config: read the field as `publicConfig` (camelCase, was the
  non-existent `public_config`) and decode its actual nested shape
  { ip4: { ip, gw }, ip6: { ip, gw }, domain } (was a flat { ipv4, ipv6, gw4, gw6 }
  that matched nothing).
- getNode location: city/country are nested under `location` on the current
  runtime (not top-level), so they were never decoded. Decode city/country/
  latitude/longitude inside `location`; drop the dead top-level country/city reads.
- getPricingPolicyById: decode the byte-encoded `name` (was returned as raw hex).

Verified live on devnet: node 50 now returns city "Bartlesville", country
"United States", public IPs/domain readable; policy 1 name "threefold_default_pricing_policy".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>